The evaluation of cellular injury produced by myocardial ischemia is often very difficult to evaluate in animal models or in man. Cultured heart cells from neonatal rats provide potential models to investigate ischemic injury at the cellular and subcellular levels. An in vitro model of ischemia will be developed to simulate the conditions produced by ischemia in animals: deprivation of oxygen and glucose and the production of lactic acidosis. Cultured muscle and endothelioid cells derived from the rat heart will serve as the principal types subjected to ischemia. Protection of the cells from the injurious effects of ischemia will be attempted with glucocorticoids and other measures. Indices of cell injury will include lysosomal and mitochondrial fragility tests, leakage of cytoplasmic enzymes into the culture medium, cell viability, functional changes in beating activity, and morphological changes in appearance.